Recently, data processing is often involved in work. Arrays are particularly common. They often need to traverse and convert them. The articles on the Internet are scattered. I have to find the Red Book and read it myself, and note it by the way to facilitate future query.
Common iteration methods for arrays
ECMAScript5 defines 5 iterative methods for arrays. Each method accepts two parameters: the function fn to run on each item and the scope object (optional) that runs the function - affecting the value of `this`.
The function (fn) passed into these methods will receive 3 parameters: item , index , array; such as:
(function(item,index,array){
//do your staff here;
},this)
Depending on the usage method, the return value after execution of this function may/do not affect the return value in the method.
The functions and return values of these 5 iteration methods are as follows:
ECMAScript5 Array element iteration method
| Method name | Method Effect | Return value |
| every() | Run the specified function for each element in the array | Boolean: If each item returns true, return true; |
| filter() | Run the specified function for each element in the array. | Array: Returns a new array composed of elements that return true when the function runs. |
| forEach() | Run the specified function for each element in the array | null: No return value |
| map() | Run the specified function for each element in the array | Array: After the return function is run, a new array composed of new elements is obtained. |
| some() | Run the specified function for each element in the array | Boolean: If any function is executed, it returns true. |
Simply put:
The every() and some() methods are suitable for conditional judgment of array elements;
filter() , map() methods are suitable for conditional filtering/reprocessing of arrays;
The forEach() method does not operate on the array itself, but only applies secondary applications to array elements;
The following are the methods of using chestnuts:
Let’s first assume a scenario where you get the company’s monthly salary list, assuming your salary is 9,000; the array of salary of company employees is salaries=[8500,12000,9900,9000],
a. Want to know if your salary is the lowest;
b. Want to know if anyone has paid as much as you;
c. Want to know if everyone is treated the same;
d. Want to exchange everyone's salary for data with K as unit
var a,b,c;
var your=9000;
var salaries=[8500,12000,9900,9000];
a=(function(item,index,array){
return item<9000
});
(a);//true;Congratulations, there are people who are lower than your salary.b=(function(item,index,array){
return item== your;
})
(b);//[9000] Haha, someone treats you the samec=(function(item,index,array){
return item==your;
});
(c);//false.Not everyone treats you the samed=(function(item,index,array){
return item/1000
});
(d);//[8.5,12,9.9,9]
The above is all the content of this article. I hope that the content of this article will help you study or work. I also hope to support me more!